1. Field of the Invention
The present invention relates to a liquid container that stores various liquids, such as ink and the like, and uniformizes the components of the liquid. In particular, the invention relates to a liquid container that is suitably used as an ink tank containing pigment ink for an ink jet printing apparatus.
2. Description of the Related Art
There is known an ink jet printing apparatus that performs printing by using pigment ink. The pigment ink contained in an ink tank is supplied from the ink tank to the ink jet printing apparatus that can eject ink. In the pigment ink, a pigment is used as a colorant, and the pigment is dispersed in an ink solvent.
A printing medium on which an image is printed by using the pigment ink has excellent light resistance and water resistance. In the pigment ink, the pigment itself is dispersed in the ink solvent as particles. Accordingly, when an ink tank (liquid container) that contains the pigment ink is left standing for many hours, the pigment in the pigment ink settles in the solvent. For example, when a printing apparatus having mounted thereon the ink tank is left standing for many hours, the pigment particles settle at the bottom surface of the ink tank. At this time, there is a concentration gradient of pigment particle from a high concentration portion at the bottom of the ink tank to a low concentration portion at the top thereof. In this state, when the pigment ink is supplied from the ink tank to print an image, the pigment concentration of the pigment ink to be supplied is ununiform, and density unevenness may occur in the printed image. Further, when the pigment ink having extremely high pigment concentration is supplied to a printing head, the coagulated pigment may be clogged in a flow passage of the printing head, and the ink cannot be ejected from the printing head.
In respect to a method that uniformizes the pigment concentration of the pigment ink in the ink tank, and homogenizes the pigment ink, Japanese Patent Laid-Open No. 2005-066520 suggests an ink tank that has a stirring member therein. The ink tank is mounted on a carriage in a serial scan type ink jet printing apparatus and reciprocates along with the carriage during a printing operation. The stirring member, which is provided in the ink tank, operates to stir the pigment ink in the ink tank using an inertial force generated when the ink tank reciprocates along with the carriage.
As such, when the stirring member carries out the stirring operation using the inertial force according to the reciprocation of the carriage, stirring of the pigment ink is quickly performed in a movement direction of the carriage in which the stirring member relatively easily moves. In Japanese Patent Laid-Open No. 2004-216761, a stirring member that operates in the same direction as the movement direction of the carriage is disclosed. However, it is necessary to provide an additional stirring member with respect to a direction perpendicular to the movement direction of the carriage.
A plurality of ink tanks, which are used in the serial scan type ink jet printing apparatus, are mounted on the carriage so as to be parallel to the movement direction of the carriage. For the sake of multicolor printing, various kinds of tanks need to be mounted on the carriage. In this case, while the width of the ink tank is set narrow in the movement direction of the carriage, the width of the ink tank is set wide in the direction crossing the movement direction of the carriage. Accordingly, in respect to the direction crossing the movement direction of the carriage, convection of the pigment ink is rarely generated.